Pressure straining device

ABSTRACT

The object of the present invention is a pressure straining device for cellulose, paper or equivalent pulp suspension, comprising at least one straining cyliner through which the acceptable pulp is strained and in connection with which there has been provided at least one blade rotating about the axis of the straining cylinder, extending over the straining surface and moving at a small distance from this surface, which blade cleans the surface of the straining cylinder facing the pulp to be strained, and which blade has a substantially drop-shaped crossed section and contains a hollow space, extending from one end to the other, for collecting pulp to be rejected, this hollow space opening through a slit towards the straining cylinder so that on either side of the slit flanges substantially pointing towards each other are produced, and said hollow space communicating at one end with a venting space, located at one end of the pressure straining device, for the pulp to be rejected. The blade has been shaped so that on its side toward the straining cylinder it substantially follows the shape of the straining cylinder, that the leading flange of the blade has been given such a direction that its forward edge is closer to the straining surface than its free rear edge and that the free forward edge of the trailing flange is located closer to the straining surface than the free rear edge of the leading flange.

United States Patent 1 Syrjanen 1 Sept. 18, 1973 PRESSURE STRAINING DEVICE [73] Assignee: Yhtyneet Paperitehtaat Osakeyhtio Jylhavaara, Valkeakoski, Finland [22] Filed: June 29, 1972 [21] Appl. No.: 267,495

[75] Inventor:

[30] Foreign Application Priority Data Primary Examiner-John Adee Attorney-Eric i-l. Waters et al.

57 ABSTRACT The object of the presentinvention is a pressure straina small distance from this surface, which blade cleans the surface of the straining cylinder facing the pulp to be strained, and which blade has a substantially dropshaped crossed section and contains a hollow space, extending from one end to the other, for collecting pulp to be rejected, this hollow space opening through a slit towards the straining cylinder so that on either side of the slit flanges substantially pointing towards each other are produced,and said hollow space communieating at one end with a venting space, located at one end of the pressurestraining'device, for the pulp to be rejected. The blade has been shaped so thaton its side toward the straining cylinder it substantially follows the rear edge and that the free forward edge of the trailing flange is located closer to the straining surface than the free rear edge of the leading flange.

2 Clainis, 3 Drawing Figures l The sorting of pulp isbased on the property of the holes in the straining cylinder that they pass, in the first place, acceptable fibres. But the size of the holes is always larger than the size of the acceptable fibres, or particles, implies, because sufficiently small holes are associated with difficulties of manufacturing technique and because-the capacity of a straining cylinder with sufficiently small holes would be substantially reduced. As a consequence the acceptable pulp always also contains particles to be rejected, fibre bundles, sticks, etc. It is in fact a characteristic of any kind of straining devices that the result of sorting is dependent on the purity of the incoming pulp. The lower the degree of purity of the arriving pulp, the lower is also that of the acceptable pulp.

It is a consequence of the mode of sorting in a straining cylinder that on its surface towards the incoming pulp there is formed a layer enriched with particles to be rejected. It is obvious that if this pulp layer can be removed as it is formed, the probability of passage of undesirable particlesdecreases. Hereby the sorting capacity of the straining cylinder is substantially increased, qualitatively above all, but also quantitatively, because now it sorts pulp of a higher degree of purity.

It is a practice known in prior art that in pressure straining devices the surface of the straining cylinder is cleaned by blades having a drop-shaped cross section. From one end to the other of the blades there extends a hollow space, which opens toward the straining cylinder through a slit, on either side of which flanges substantially pointing towards each other are. formed. However, a blade of this kind has the drawback that the mutual distance of the blade and the straining surface increases towards the trailing edge. of the blade. The pulp. flow is thenso directed that part of the acceptable pulp which has already passed through the straining surface returns to the other side of the straining surface. Furthermore, the blade of prior arthas the drawback that the free edges, of the flanges on both sides of the slit are at equaldistances from the straining surface.

The pulp to be rejected will then not all departthrough the hollow space within the blade; instead, this pulp flow is divided, to passon either side of the rearflange, so that part of the pulp to be rejected remains admixed with the pulp to be sorted.

The aim of the present invention is to eliminate the drawbacks pointed out above. The invention is characterized in that the blade has been shaped so that on its side toward the straining cylinder it substantially followsthe shape of the straining cylinder, that the leading flange of the blade has been given a direction such that its forward edge is closer to the straining surface than its free rear edge, and that the free forward edge of the trailing flange is located closer to the straining surface than the free rear edge of the leading flange. In. that case the leading flange will direct the flow of the pulp to be rejected into the hollowspace within the blade and thence further to. the rejected pulp voiding space.

The invention is described in the following by the aid.

2 FIG. 3 shows the section along the line III-III in F IG. 2.

Pulp suspension is introduced, under pressure, tangentially by the pipe 11 into the annular space 12, which is confined externally by the mantle 13 of the pressure straining device and internally by the straining of an example, with-reference to the attached drawing,

wherein I FIG. 1 presentsthe pressure straining device, partly in axial section,

FIG. 2 shows. the straining cylinder-and blades belonging to the straining device, inperspective, and.

cylinder 1. Theblades 2 have been mounted on the ends of a transversal arm 14, which rotates along with the shaft 15.

The acceptable pulp passes through the straining cylinder 1 from the annular space 12 to the inside of the straining surface and thence further through the pipe 16 to a conversion stage. At the same time, while the acceptable pulp flows through the straining cylinder, on its outer surface a pulp layer enriched with particles to be rejected is formed, which in accordance with FIG. 3 is carried into the hollow space 3 within the blade 2 and thence further to the rejected pulp voiding space 6.

In FIG. 3 the cross'section of the blade 2 has been shown, revealing that the cross section has substantially drop-shaped form, however so that one side of it substantially adheres to the shape of the straining cylinder 1. The leading flange 4 of the blade 2 has been given a direction such that its front edge 7 is closer to the straining surface than its free rear edge 8. The trailing flange 5 has been placed so that its free front edge 9 is approximately the same distance from the straining surface 1 as the front edge 7 of the leading flange 4. When the pressure straining device is in operation, a pulp layer enriched with particles to be rejected is produced on the side of the strainingcylinder 1 towards the blade 2. The direction of the leading flange 4 and the position of the front edge 9 of the trailing flange 5 have the result that this pulpto be rejected is carried into the ho]- low space 3 within the blade 2 and further to the voiding space 6. The front edge 9 of the trailing flange 5 has furthermore been rounded sothat it does not constitute any objectionable sharp point on which fibres might become stuck. The rear flange 5 may also be directed so that its rear edge 10 is somewhat farther away from the straining surface than its free front edge 9, in order that the pulp might not be packed in the'narrow gap remaining between this flange 5 and the straining surface 1.

It is obvious to one skilled in the art that various embodiments of the invention may vary within the scope of the patent claimspresented below. For instance, there may be several straining cylinders, which have been concentrically mounted andin connection with each of which. at least one blade has been provided. Also the number of blades in connection with one straining cylinder is not confined in any way. Substan-' tial things are the crosssectional shape of the blade and the. direction. of the flanges oneither side of the slit. The substantially drop-shaped blade cross section shouldalso be understood. as a general shape which is favourable in view of flow, and in this shape the thickness, roundings, etc. may vary.

1. Improvement in a pressure straining device for cellulose, paper or equivalent pulp suspension, comprising at least one straining cylinder through which the acceptable pulp is strained and inconnection with which there has been provided at least one blade rotating about the axis of the straining cylinder, extending over the straining surface and: moving at a small distance from this surface, which blade cleans the-surface of the straining cylinder facing the pulp to be strained, and which blade has a substantially drop-shaped cross section and contains a hollow space, extending from one end to the other, for collecting pulp to be rejected, this hollow space opening through a slit towards the straining cylinder so that on either side of the slit flanges, substantially pointing towards each other are produced, and said hollow space communicating at one end with a voiding space for the pulp to be rejected, located at one end of the pressure straining device, wherein the improvement comprises that the blade has been shaped so that on its side towards the straining cylinder it substantially follows the shape of the strainis located closer to the straining surface than its rear edge.

a: a: a: a: 

1. Improvement in a pressure straining device for cellulose, paper or equivalent pulp suspension, comprising at least one straining cylinder through which the acceptable pulp is strained and in connection with which there has been provided at least one blade rotating about the axis of the straining cylinder, extending over the straining surface and moving at a small distance from this surface, which blade cleans the surface of the straining cylinder facing the pulp to be strained, and which blade has a substantially drop-shaped cross section and contains a hollow space, extending from one end to the other, for collecting pulp to be rejected, this hollow space opening through a slit towards the straining cylinder so that on either side of the slit flanges, substantially pointing towards each other are produced, and said hollow space communicating at one end with a voiding space for the pulp to be rejected, located at one end of the pressure straining device, wherein the improvement comprises that the blade has been shaped so that on its side towards the straining cylinder it substantially follows the shape of the straining cylinder, that the leading flange of the blade has been given such a direction that its forward edge is closer to the straining surface than its free rear edge and that the free forward edge of the trailing flange is located closer to the straining surface than the free rear edge of the leading flange.
 2. Pressure straining device according to claim 1, characterized in that the trailing flange of the blade has been given a direction such that its free forward edge is located closer to the straining surface than its rear edge. 